Clever coating opens door to smart windows

Researchers from RMIT University have developed a new ultra-thin coating that responds to heat and cold, opening the door to “smart windows”.

The self-modifying coating, a thousand times thinner than a human hair, works by automatically letting in more heat when it’s cold and blocking the sun’s rays when it’s hot. Smart windows have the ability to naturally regulate temperatures inside a building, leading to major environmental benefits and significant financial savings.

The self-regulating coating is created using a material called vanadium dioxide. The coating is 50-150 nanometres in thickness. At 67 degrees Celsius, vanadium dioxide transforms from being an insulator into a metal, allowing the coating to turn into a versatile optoelectronic material controlled by, and sensitive to light. The coating stays transparent and clear to the human eye but goes opaque to infra-red solar radiation, which humans cannot see and is what causes sun-induced heating.

Until now, it has been impossible to use vanadium dioxide on surfaces of various sizes because the placement of the coating requires the creation of specialised layers, or platforms. The RMIT researchers have developed a way to create and deposit the ultra-thin coating without the need for these special platforms – meaning it can be directly applied to surfaces like glass windows.

“We are making it possible to manufacture smart windows that block heat during summer and retain heat inside when the weather cools,” says Bhaskaran. “We lose most of our energy in buildings through windows. This makes maintaining buildings at a certain temperature a very wasteful and unavoidable process.

“Our technology will potentially cut the rising costs of air-conditioning and heating, as well as dramatically reduce the carbon footprint of buildings of all sizes. Solutions to our energy crisis do not come only from using renewables; smarter technology that eliminates energy waste is absolutely vital.”

Smart glass windows are about 70% more energy efficient during summer and 45% more efficient in the winter compared to standard dual-pane glass. New York’s Empire State Building reported energy savings of US$2.4m and cut carbon emissions by 4,000 tonnes after installing smart glass windows. This was using a less effective form of technology.

“The Empire State Building used glass that still required some energy to operate,” Bhaskaran says. “Our coating doesn’t require energy and responds directly to changes in temperature.”

Co-researcher and PhD student Mohammad Taha says that while the coating reacts to temperature it can also be overridden with a simple switch.

“This switch is similar to a dimmer and can be used to control the level of transparency on the window and therefore the intensity of lighting in a room,” Taha says. “This means users have total freedom to operate the smart windows on-demand.”

The technology can also be used to control non-harmful radiation that can penetrate plastics and fabrics. This could be applied to medical imaging and security scans. Bhaskaran says that the team was looking to roll the technology out as soon as possible.

“The materials and technology are readily scalable to large area surfaces, with the underlying technology filed as a patent in Australia and the US,” she said.